text: Mutations in the CYC1 gene are associated with mitochondrial complex III deficiency nuclear type 6. The disease symptoms include early childhood onset of severe lactic acidosis and ketoacidosis, usually in response to infection. Insulin-responsive hyperglycemia is also present, but psychomotor development appears normal. Mutation of CYC1 was observed to cause instability in the cytochrome b-c1 complex, which decreased its ability to create energy through oxidative phosphorylation. Mitochondrial complex III deficiency nuclear type 6 is autosomal recessive.